An ever increasing number of engines having a starter-generator unit have been developed since the 1990s in order to improve fuel mileage. In such engines, the combustion process is stopped when the vehicle comes to rest, for example, at a stoplight. In this condition the starter-generator unit is operated as a starter motor to restart the engine. Once the engine is started, the starter-generator unit can be selectively operated as a generator to recharge the batteries.
The starter-generator unit is mechanically connected to the engine via an endless drive such as a belt or chain. The endless drive is subject to tension fluctuations, particularly as the starter-generator unit shifts its function between starter and generator, in which case the tight side and slack side of the endless drive reverses. The endless drive tensioning system must handle this and other tension fluctuations that occur whilst the engine is operating.
Various dual arm tensioners are known in the art, example of which are found in publication numbers DE 102 53 450 A1; EP 1 464 871 A1; US 2004/0171448 A1; EP 1 122 464 A1; and DE 42 43 451 A1. However, a tensioner disclosed herein seeks to provide a more robust solution to effectively compensating for longitudinal shifts occurring in portions of the endless drive as a result of a changeover between the tight side and the slack side.